Methods and apparatus for temperature control of devices and mechanical resonating structures

ABSTRACT

Methods and apparatus for temperature control of devices and mechanical resonating structures are described. A mechanical resonating structure may include a heating element and a temperature sensor. The temperature sensor may sense the temperature of the mechanical resonating structure, and the heating element may be adjusted to provide a desired level of heating. Optionally, additional heating elements and/or temperature sensors may be included.

RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §120 as acontinuation of U.S. patent application Ser. No. 12/781,076, filed May17, 2010 under Attorney Docket No. G0766.70008US01, and entitled“METHODS AND APPARATUS FOR TEMPERATURE CONTROL OF DEVICES AND MECHANICALRESONATING STRUCTURES,” which claims the benefit under 35 U.S.C. §119(e)of U.S. Provisional Patent Application Ser. No. 61/184,167, filed onJun. 4, 2009 under Attorney Docket No. G0766.70008US00, and entitled“METHODS AND APPARATUS FOR TEMPERATURE CONTROL OF DEVICES AND MECHANICALRESONATING STRUCTURES,” both of which are hereby incorporated herein byreference in their entireties.

BACKGROUND

1. Field

The technology described herein relates to temperature control ofdevices and mechanical resonating structures.

2. Related Art

Resonators can be used to produce a resonance signal, and can generallybe mechanical, electrical, or electromechanical. Electromechanicalresonators include a mechanical resonating structure configured tovibrate in at least one dimension, which vibration is used to generate acorresponding electrical signal. The mechanical resonating structure isgenerally connected at one or more points to a fixed support, whichkeeps the mechanical resonating structure properly positioned, and canprovide mechanical support.

Devices having mechanical resonating structures are prone to temperatureinduced variations in their operation due to temperature inducedvariations in one or more components of the device, such as themechanical resonating structure. The mechanical resonating structure hasan inherent resonance frequency determined by factors such as its size,shape, and material. One or more of the factors determining the inherentresonance frequency of the mechanical resonating structure may betemperature dependent, thus giving rise to a temperature dependence ofthe resonance frequency. In addition, any circuitry connected to themechanical resonating structure (e.g., driving and/or detectioncircuitry) may itself have temperature dependent characteristics, suchas temperature dependent capacitances and/or inductances. Any suchtemperature dependent characteristics of circuitry connected to themechanical resonating structure can also impart a temperature dependenceto the resonance frequency of the mechanical resonating structure.

SUMMARY

According to one aspect, a temperature compensatedmicroelectromechanical systems (MEMS) resonating device is provided. Thetemperature compensated MEMS resonating device comprises a semiconductorsubstrate and a suspended micromechanical resonating structure coupledto the semiconductor substrate by two or more flexible anchors. Thetemperature compensated MEMS resonating device further comprises atleast one first electrode mechanically coupled to the suspendedmicromechanical resonating structure and configured to provide anelectrical drive signal to the suspended micromechanical resonatingstructure to excite vibration of the suspended micromechanicalresonating structure. The temperature compensated MEMS resonating devicefurther comprises at least one second electrode mechanically coupled tothe suspended micromechanical resonating structure and configured tosense the vibration of the suspended micromechanical resonatingstructure and produce an output signal indicative of the vibration. Thetemperature compensated MEMS resonating device further comprises aheating element formed on the suspended micromechanical resonatingstructure and coupled to control circuitry configured to control anamount of electrical current passing through the heating element, and atemperature sensor formed on the suspended micromechanical resonatingstructure and configured to provide a temperature output signalindicative of a temperature of the suspended micromechanical resonatingstructure. The temperature sensor and heating element are coupledtogether in a feedback loop comprising the control circuitry.

According to another aspect, a device comprises a mechanical resonatingstructure including a heating element configured to control atemperature of the mechanical resonating structure, and a temperaturesensor configured to detect the temperature of the mechanical resonatingstructure. The mechanical resonating structure is formed at leastpartially of a piezoelectric material.

According to another aspect, a device comprises a substrate having afront surface and a back surface. The device further comprises amechanical resonating structure formed on the front surface of thesubstrate. The device further comprises a heating element formed on orwithin the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the technology will be described in connectionwith the following figures. It should be appreciated that the figuresare not necessarily drawn to scale, and are intended for purposes ofillustration only. The same reference number in multiple figuresidentifies the same item.

FIG. 1 is an example of a cross-section of a device comprising amechanical resonating structure including a heating element and atemperature sensor, according to one embodiment of the technology.

FIG. 2 is a perspective view of a non-limiting example of the mechanicalresonating structure of FIG. 1.

FIGS. 3A-3C illustrate alternative configurations of a heating elementof a mechanical resonating structure, according to various non-limitingembodiments of the technology.

FIG. 4 illustrates a non-limiting example of a configuration of aheating element and temperature sensor of a mechanical resonatingstructure, according to one embodiment of the technology.

FIG. 5 is an electromechanical circuit diagram of a device providingtemperature control functionality, according to one non-limitingembodiment of the technology.

FIGS. 6A-6B illustrate non-limiting examples of packaged devicesincluding the device 100 of FIG. 1, according to different embodimentsof the technology.

DETAILED DESCRIPTION

Structures and methods for controlling the temperature of devices andmechanical resonating structures are described. In some aspects, thedevices may include a mechanical resonating structure, which itself mayinclude a heating element and a temperature sensor. The heating elementand the temperature sensor of the mechanical resonating structure mayfacilitate maintaining the temperature of the mechanical resonatingstructure at a desired value, which may facilitate control of aresonance frequency of the mechanical resonating structure. The devicemay optionally include additional heating elements and/or temperaturesensors, for example to control the temperature of circuitry connectedto the mechanical resonating structure.

When a first structure is described as including a second structure inthe present application (e.g., a mechanical resonating structureincluding a heating element), it should be understood that the secondstructure can be within (including partially or completely within) thefirst structure, integrated with the first structure, or on the firststructure. When a structure (e.g., layer, region, etc.) is referred toas being “on”, “over” or “overlying” another structure, it can bedirectly on the structure, or an intervening structure (e.g., layer,region) also may be present. A structure that is “directly on” or “incontact with” another structure means that no intervening structure ispresent. It should also be understood that when a structure is referredto as being “on”, “over”, “overlying”, or “in contact with” anotherstructure, it may cover the entire structure or a portion of thestructure.

The aspects described above, as well as additional aspects of thetechnology, will now be further described. It should be appreciated thatthese aspects may be used individually, all together, or in anycombination of two or more, as the technology described herein is notlimited in this respect.

FIG. 1 illustrates a cross-sectional view of a device including amechanical resonating structure having a heating element and atemperature sensor, according to one non-limiting embodiment. The device100 includes a mechanical resonating structure 102, which itselfincludes a heating element 104, a temperature sensor 106, and one ormore electrodes 108. The mechanical resonating structure 102 isconnected to and, in the non-limiting example of FIG. 1, suspended abovea substrate 110, thus creating a gap 111. A heating element 112 isoptionally formed on a backside of the substrate 110. The substrate 110is bonded to a cap wafer 114 by a bonding layer 116. In the non-limitingexample of FIG. 1, the cap wafer 114 includes integrated circuitry 118,and also optionally includes a heating element 120 and a temperaturesensor 122. The mechanical resonating structure 102 is separated fromthe cap wafer 114 in the non-limiting example of FIG. 1 by a gap 124. Insome embodiments, the mechanical resonating structure is inside a vacuumenvironment.

For purposes of illustration, a perspective view of an example of asuitable mechanical resonating structure 102 (in the absence of many ofthe surrounding structures illustrated in FIG. 1) is shown in FIG. 2. Asshown, the mechanical resonating structure 102 is substantially planarin this non-limiting embodiment, and has a length L, a width W, and athickness T. It may be connected to the substrate 110 by anchors 202 aand 202 b, although any number of anchors (e.g., two or more), may beused, one or more of which may be flexible in some embodiments. Itshould be appreciated that various types of mechanical resonatingstructures may be employed, and that the example illustrated in FIG. 2is provided merely for purposes of explanation.

The heating element 104 and the temperature sensor 106 may allow forcontrol of the temperature of the mechanical resonating structure 102.For example, the heating element 104 may heat the mechanical resonatingstructure 102 and the temperature sensor 106 may sense the temperatureof the mechanical resonating structure 102. The heating element andtemperature sensor may be connected to temperature control circuitry(e.g., integrated circuitry 118, or any other suitable circuitry), whichmay process the output of the temperature sensor and determine whetherthe sensed temperature is at a desired value. Depending on the value ofthe temperature of the mechanical resonating structure, as sensed by thetemperature sensor 106, the heating element may be controlled (e.g., viaa control signal from the temperature control circuitry) to apply moreor less heat (e.g., by adjusting an amount of electrical current flowingthrough the heating element, or in any other suitable manner), to bringthe temperature of the mechanical resonating structure 102 to a desiredvalue. In some embodiments, the heating element 104 and the temperaturesensor 106 may form part or all of a temperature control feedback loop.In some embodiments, the temperature control circuitry may be part ofsuch a feedback loop.

The heating element 104 and the temperature sensor 106 may be anysuitable structures for performing their respective functions. Forexample, the heating element 104 may have any suitable size, shape,material, and positioning. It may be formed by one or more electrodes,conductive traces (e.g., metal conductive traces, doped semiconductortraces (e.g., doped silicon), etc.), one or more doped regions (e.g.,doped regions of a piezoelectric material in those embodiments in whichthe mechanical resonating structure comprises one or more piezoelectricmaterials), or any other suitable structures. In some embodiments, theheating element 104 may be a bulk heater, formed by implanting thesurface of a structure (e.g., a surface of mechanical resonatingstructure 102) with any suitable dopant to make the surface conductive.FIGS. 3A-3C illustrate non-limiting examples of suitable configurationsof heating element 104.

FIG. 3A is a simplified perspective view of a mechanical resonatingstructure 302 (in the absence of surrounding structures), which maycorrespond to the mechanical resonating structure 102 of FIG. 1, and aheating element 304 a, which may correspond to the heating element 104.As shown, the heating element 304 a is formed of multiple segments on asurface of the mechanical resonating structure 302. The heating element304 a may be formed of metal traces, doped regions, or any othersuitable materials.

FIG. 3B illustrates an alternative configuration of a heating element ofthe mechanical resonating structure 302. As shown, the heating element304 b forms a serpentine structure on a surface of the mechanicalresonating structure 302.

FIG. 3C illustrates a further alternative arrangement of a heatingelement of a mechanical resonating structure. The mechanical resonatingstructure 302 includes two transducers 303 a and 303 b, each of which isformed by two electrodes, 305 a and 305 b for transducer 303 a, and 307a and 307 b for transducer 303 b. As will be described below, themechanical resonating structures described herein may be piezoelectricstructures, and transducers (e.g., transducers 303 a and 303 b in FIG.3C) may actuate and detect vibration of the mechanical resonatingstructures. In FIG. 3C, the heating element 304 c assumes a zigzagshape, passing between the transducers 303 a and 303 b.

It should be appreciated from the foregoing description and figures thatthe heating elements of mechanical resonating structures describedherein may have any suitable size, shape, and positioning, and that thevarious aspects of the technology are not limited in this respect. Itshould also be appreciated that the heating elements 104 and 304 a-304 cmay be formed on, or within the corresponding mechanical resonatingstructures. One example in which a heating element may be within amechanical resonating structure is when the mechanical resonatingstructure is formed of multiple (e.g., three or more) layers (e.g., anactive layer and one or more inactive layers), with the heating elementcomprising one of the layers, and being positioned between two otherlayers of the mechanical resonating structure. Thus, the examples ofFIGS. 3A-3C, in which the heating elements are formed on a surface ofthe mechanical resonating structure 302, are non-limiting examples.

Similar to the heating element 104, the temperature sensor 106 may haveany suitable size, shape, material, and positioning. For example, thetemperature sensor 106 may have any of the shapes previously describedwith respect to the heating elements in FIGS. 3A-3C, or any othersuitable shapes. As with the heating element 104, the temperature sensor106 may be formed of one or more electrodes, conductive traces, dopedregions, or any other suitable structures.

The temperature sensor 106 and heating element 104 may have any suitablepositioning relative to each other. According to some embodiments, theheating element 104 and temperature 106 may be positioned to have a goodthermal path between them (i.e., a thermally conductive path betweenthem). In some embodiments, the temperature sensor may be positioned onthe same side (e.g., on a same surface) of the mechanical resonatingstructure as the heating element. In other embodiments, the heatingelement and temperature sensor may be formed on opposite sides (e.g.,opposing surfaces) of the mechanical resonating structure. In someembodiments, the temperature sensor 106 and/or heating element may beformed within the mechanical resonating structure. For example,according to one embodiment, the heating element may be a bulk heaterand the temperature sensor may be formed on a surface of the mechanicalresonating structure (e.g., in the center of the mechanical resonatingstructure), separated from the bulk heater by a layer of material (e.g.,an insulating layer). Either or both of the heating element andtemperature sensor may be on a vibrating portion of the mechanicalresonating structure and/or a fixed portion of the mechanical resonatingstructure. Other configurations are also possible.

The temperature sensor 106 and heating element 104 may be separated byany suitable distance(s). The distance of separation may be limited bythe size of the mechanical resonating structure. For example, in someembodiments, the heating element 104 and temperature sensor 106 areseparated by the maximum dimension of the mechanical resonatingstructure. Thus, in some embodiments, the heating element andtemperature sensor may be separated by 2 mm or less. In someembodiments, the heating element and temperature sensor are separated byless than 1 mm, or less than 100 microns. In some embodiments, theheating element and temperature sensor may be separated by as small adistance as possible while remaining electrically isolated from eachother. For example, the heating element and temperature sensor may beseparated by a thin layer of material (e.g., an insulating material) insome embodiments, which may have a thickness of less than 200 microns,less than 100 microns, less than 50 microns (e.g., 25 microns), lessthan 10 microns (e.g., 5 microns, 4 microns, etc.), or any othersuitable thickness. From the foregoing, it should be appreciated thatthe distance of separation may depend on a particular application of thedevice, the dimensions of the mechanical resonating structure, or otherfactors.

FIG. 4 illustrates a perspective view of a non-limiting example of themechanical resonating structure 302 having a heating element 404(corresponding to the heating element 104 of FIG. 1) and a temperaturesensor 406 (corresponding to the temperature sensor 106 of FIG. 1). Asshown, heating element 404 and temperature sensor 406 are formed on asame surface of the mechanical resonating structure 302, with thetransducers 303 a and 303 b formed therebetween. Other configurationsare also possible, as FIG. 4 is merely an example.

According to some embodiments, additional heating and/or temperaturesensing functionality may be provided for the device 100. For example,while heating element 104 provides heating at the position of themechanical resonating structure 102, some embodiments may also includeone or more structures to provide heating at other positions of thedevice 100 and/or on a different scale. For example, some embodimentsmay provide heating over a larger area of device 100 than that providedby the heating element 104. In some embodiments, one or both of heatingelements 112 and 120 may be provided with the device 100. As shown inFIG. 1, the heating element 112 may be located on a backside of thesubstrate 110. Alternatively, the heating element 112 may be positionedon a top side of the substrate 110, e.g., below the mechanicalresonating structure 102, or within (including partially or completelywithin) the substrate 110. In some embodiments, multiple heatingelements may be provided with the substrate 110, e.g., heating element112 on the backside, a heating element on the top side, and a heatingelement within the substrate. In some embodiments, the heating element112 may be positioned and sized to improve the temperature uniformitywithin the device 100, e.g., in and around the mechanical resonatingstructure 102.

The heating element 112 may have any suitable size, shape, and material.For example, the heating element 112 may cover all or only a portion ofthe backside of substrate 110 (in those embodiments in which the heatingelement 112 is on the backside of substrate 110). Its shape may be thesame as any of those previously described with respect to heatingelement 104 (e.g., the shapes illustrated in FIGS. 3A-3C, and FIG. 4),or any other suitable shape. The heating element 112 may be formed byone or more electrodes, conductive traces (e.g., metal traces, dopedsemiconductor traces, etc.), doped regions of a material, or may haveany other suitable form.

The heating element 120 may be used to maintain the integrated circuitry118 on the cap wafer at a desired temperature, may be used to providemore uniform heating in and around the mechanical resonating structure102, or may be used for any other reason. As shown, in the non-limitingexample of FIG. 1, the heating element 120 is located on a backside ofthe cap wafer 114. Alternatively, the heating element 120 may be withinthe cap wafer 114. As with the heating element 112, the heating element120 may have any suitable size, shape, and material, including any ofthose previously described with respect to heating elements 104 and 112,or any other size, shape, and/or material.

It should be appreciated that devices employing one or more of thetechniques described herein may include and use any combination ofheating elements 104, 112, and 120. For example, in some embodiments, adevice may include only heating element 104. In other embodiments, adevice may include heating elements 104 and 120. In some embodiments, adevice may include only heating elements 112 and 120. Other combinationsare also possible, and the various aspects described herein are notlimited to the inclusion of all three of the illustrated heatingelements.

According to some aspects, discrete temperature control may be providedto subsystems, or zones, within the device 100. For example, accordingto one aspect, discrete temperature control of the mechanical resonatingstructure 102 and the integrated circuitry 118 is provided. In oneembodiment of such a device, temperature control of the mechanicalresonating structure 102 may be provided using the heating element 104and the temperature sensor 106, as previously described. Temperaturecontrol of the integrated circuitry 118 may be provided using theheating element 112 and/or 120 and temperature sensor 122. Thetemperature sensor 122 may be shaped, sized, and positioned toaccurately sense the temperature of the integrated circuitry 118 (e.g.,by sensing the temperature in the vicinity of the integrated circuitry118), and the heating element 112 and/or 120 may be controlled, based atleast partially on the output of the temperature sensor 122, to providemore or less heat. For example, an output signal of temperature sensor122 may be provided to temperature control circuitry (e.g., integratedcircuitry 118, or any other suitable circuitry), which may process theoutput signal and determine whether the sensed temperature is at adesired value. Depending on the value of the temperature of theintegrated circuitry, as sensed by the temperature sensor 122, theheating element 112 and/or 120 may be controlled (e.g., via a controlsignal from the temperature control circuitry) to apply more or lessheat (e.g., by adjusting an amount of electrical current flowing throughthe heating element), to bring the temperature of the integratedcircuitry 118 to a desired value. In some embodiments, the heatingelement 120 and the temperature sensor 122 may form part or all of atemperature control feedback loop. In some embodiments, the temperaturecontrol circuitry may be part of such a feedback loop. Thus, differenttemperatures may be maintained for the mechanical resonating structureand the integrated circuitry by suitable use of the heating elements104, 112, and/or 120, and the temperature sensors 106 and/or 122.According to some embodiments, the temperature sensor 122 is positionedas close to the thermal center of the device as possible.

According to some embodiments in which distinct temperature zones aremaintained, such zones may be maintained at any suitable temperatures.For example, one or more temperature zones of a device may be maintainedat a temperature based on a maximum expected operating temperature ofthe device. One or more temperature zones may be maintained at atemperature corresponding to a temperature at which a minimum change infrequency of the device is experienced for a change in temperature. Onetechnique for compensating for temperature induced variations in theresonance frequency of a device is to heat the device to a temperatureat which the temperature dependence of the resonance frequency of thedevice is a minimum. The amount of change of the resonance frequency ofa device for a unit change in temperature may not be constant fordevices having mechanical resonating structures. Rather, the amount ofchange of the resonance frequency for a unit change in temperature maybe variable. By heating the device to a temperature at which the amountof change in the resonance frequency for a unit change in temperature isa minimum, the impact of any subsequent temperature variations may beminimized.

According to one embodiment, distinct temperature zones are maintainedwithin the device 100. An “outer” temperature zone targets thetemperature of the integrated circuitry 118, while an “inner”temperature zone targets the mechanical resonating structure 102. Theouter temperature zone may be maintained at a temperature lower thanthat of the inner temperature zone. According to one embodiment, theouter temperature zone (e.g., targeting integrated circuitry of adevice) may be maintained at a temperature intended to preventoverheating of certain components within the device. For example,integrated circuitry may be adversely affected if overheated. Therefore,a temperature zone targeting the integrated circuitry of a device may bemaintained to prevent any adverse temperature-induced behavior on theintegrated circuitry. According to one embodiment, the outer temperaturezone may be maintained at a temperature equal to or above that of themaximum expected operating temperature of the device.

According to one embodiment, the integrated circuitry 118 of device 100is maintained at a temperature in the range of approximately 60-100° C.(e.g., 85-95° C., e.g., 90° C.), while the mechanical resonatingstructure 102 is maintained at approximately 65-110° C. (e.g., 90-100°C., e.g., 95° C.). Other values are also possible, as the variousaspects described herein relating to maintaining discrete temperaturezones within a device are not limited to maintaining any particulartemperature values. As mentioned, according to some embodiments, one ormore zones of a device may be heated to a temperature above the maximumexpected operating temperature of the device. For example, the maximumexpected operating temperature of the device 100 for some applicationsmay be 85° C. The integrated circuitry 118 may be maintained, in someembodiments, at 90° C. using one or more of the techniques describedherein, and the mechanical resonating structure may be maintained atapproximately 95° C. using one or more of the techniques describedherein. In this manner, the impact of temperature variations duringoperation of the device 100 may be minimized.

FIG. 5 illustrates an electromechanical circuit schematic of a device500 providing temperature control functionality. The device 500comprises a mechanical resonating structure 502, which may be, forexample, the mechanical resonating structure 102 of FIG. 1, or any othersuitable mechanical resonating structure. The mechanical resonatingstructure 502 may be coupled to and controlled by driving, sensing, andcontrol circuitry 503. The mechanical resonating structure may include aheating element 504 (e.g., the heating element 104 of FIG. 1, or anyother suitable heating element) and a temperature sensor 506 (e.g., thetemperature sensor 106 of FIG. 1, or any other suitable temperaturesensor). The heating element 504 and temperature sensor 506 may beconfigured in a feedback loop with temperature control circuitry 505,which may be any suitable temperature control circuitry for receiving asignal from the temperature sensor 506 and controlling the heatingelement 504. The device 500 further comprises a heating element 520(e.g., heating element 112 and/or heating element 120 of FIG. 1, or anyother suitable heating element) and a temperature sensor 522 (e.g.,temperature sensor 122 of FIG. 1, or any other suitable temperaturesensor), which are configured in a feedback loop with temperaturecontrol circuitry 507. The temperature control circuitry 507 may be anysuitable circuitry for receiving a signal from the temperature sensor522 and controlling the heating element 520.

The mechanical resonating structure 502 may be controlled by thedriving, sensing, and control circuitry 503. For example, the driving,sensing, and control circuitry 503 may actuate and/or sense/detectvibration of the mechanical resonating structure, and may be anysuitable circuitry for doing so. In some embodiments, the driving,sensing, and control circuitry 503 may include one or more components ofintegrated circuitry 118 in FIG. 1.

The heating element 504, temperature sensor 506, and temperature controlcircuitry 505 are configured in a feedback loop in the non-limitingexample of FIG. 5. The temperature sensor 506 may sense the temperatureof the mechanical resonating structure 502, and provide an output signalto the temperature control circuitry 505. Depending on the value of thesensed temperature, the temperature control circuitry may control theheating element 504 to apply more or less heat to the mechanicalresonating structure (e.g., by adjusting the amount of electricalcurrent flowing through the heating element, or in any other suitablemanner) to adjust the temperature of the mechanical resonatingstructure.

Similarly, the heating element 520, temperature sensor 522, andtemperature control circuitry 507 are configured in a feedback loop, andmay control the temperature of one or more portions of the device 500.The temperature sensor 522 may sense the temperature of the portion ofinterest of the device 500 (e.g., the temperature in the vicinity ofintegrated circuitry of the device 500, or any other portion ofinterest) and provide an output signal to the temperature controlcircuitry 507. Depending on the value of the sensed temperature, thetemperature control circuitry 507 may control the heating element 520 toapply more or less heat.

It should be appreciated that the driving, sensing, and controlcircuitry 503, the temperature control circuitry 505, and thetemperature control circuitry 507 may be realized in any suitablemanner. For example, in some embodiments, these three circuits may bedistinct from each other. In other embodiments, two or more of thesethree circuits may share one or more components. For example, in someembodiments, the temperature control circuitry 505 and the temperaturecontrol circuitry 507 may form a single temperature control circuit. Insome embodiments, one or more of the driving, sensing, and controlcircuitry 503, the temperature control circuitry 505, and thetemperature control circuitry 507 may employ one or more components ofintegrated circuitry 118 of FIG. 1. Other configurations are alsopossible.

According to some embodiments, devices of the type described herein maybe packaged. The packaging may facilitate maintaining the device at auniform temperature, and in some embodiments may be formed byovermolding. FIGS. 6A and 6B illustrate non-limiting examples. As shownin FIG. 6A, the packaged device 600 a includes the device 100 of FIG. 1mounted on a chip 602. The chip 602, which includes heating elements 604a and 604 b, is housed within a plastic package 606. The device 100 andchip 602 may be configured to be approximately in the center of thepackage or molding (e.g., at the thermal center) to facilitatemaintaining a uniform temperature. The packaging or overmolding may beformed from any suitable material. Suitable materials can includeinsulating materials, such as aerogels, epoxies, and polymericmaterials, amongst others. The package 606 may take any suitable shape,as the aspects in which devices are packaged are not limited in thisrespect.

The heating elements 604 a and 604 b may facilitate temperature controlwithin the package 606. They may therefore be any suitable type ofheating elements, such as any of the types previously described withrespect to device 100, or any other suitable heating elements.

Electrical access to the chip 602 and device 100 may be provided byelectrical leads 608 a and 608 b, which in some embodiments may be asthin as possible, for example to minimize the thermal conductivity ofthe leads. Any suitable type of electrical connections may be used,including bond wires, a lead frame, or any other suitable types ofelectrical connection, as the various aspects relating to packageddevices are not limited in this respect.

FIG. 6B illustrates an alternative form of a packaged device. Thepackaged device 600 b includes the device 100 of FIG. 1 within thepackage (or overmolding) 610. The device 100 may be positionedapproximately at the center of the package 610 to facilitate maintaininga uniform temperature. Electrical access to the device 100 may beprovided by the electrical pins 612 a and 612 b, which are connected tothe device 100 by respective bond wires 614 a and 614 b. Other mannersof providing electrical access are also provided. The package 610, whichagain may be overmolding in some embodiments, may be formed of anysuitable material(s), including aerogel, epoxy mold, or any othersuitable material.

It should be appreciated from the foregoing that one or more of thestructures and/or techniques described herein may be used to allow forcontrolled heating of a device and/or a mechanical resonating structureof a device. Thus, the device and/or mechanical resonating structure ofa device may be heated to a temperature value at which deviations fromthat temperature value have minimal impact on the operation of thedevice and/or mechanical resonating structure, e.g., on the resonancefrequency of the mechanical resonating structure. Thus, devices such asthose described herein may be provide a stable resonance frequency insome embodiments.

One or more of the techniques described herein may provide accuratetemperature control. For example, temperature control with +/−0.1-0.001°C. (e.g., +/−0.01° C.) accuracy may be achieved using one or more of thetechniques described herein. In addition, one or more of the techniquesmay provide for stable temperature control (i.e., maintaining atemperature at a substantially constant value).

As mentioned, the various aspects described herein are not limited touse with any particular mechanical resonating structures. Rather, theillustration of mechanical resonating structures 102 and 302 areprovided merely for purposes of illustration of suitable mechanicalresonating structures. However, it should be appreciated that themechanical resonating structures (e.g., mechanical resonating structure)may be of any suitable type, as the various aspects of the technologyare not limited in this respect. Thus, aspects of the technology mayapply to mechanical resonating structures of variousmaterials/compositions, shapes, sizes, and/or methods of actuationand/or detection. In addition, aspects of the technology may apply todevices including various types of mechanical resonating structures,such as resonators, filters, sensors, or other suitable structures.

For example, the mechanical resonating structure may comprise or beformed of any suitable material(s) and may have any composition.According to some embodiments, the mechanical resonating structure maycomprise or be formed of a piezoelectric material. According to someembodiments, the mechanical resonating structure comprises quartz,LiNbO₃, LiTaO₃, aluminum nitride (AlN), or any other suitablepiezoelectric material (e.g., zinc oxide (ZnO), cadmium sulfide (CdS),lead titanate (PbTiO₃), lead zirconate titanate (PZT), potassium niobate(KNbO₃), Li₂B₄O₇, langasite (La₃Ga₅SiO₁₄), gallium arsenside (GaAs),barium sodium niobate, bismuth germanium oxide, indium arsenide, indiumantimonide), either in substantially pure form or in combination withone or more other materials. Moreover, in some embodiments in which themechanical resonating structure comprises a piezoelectric material, thepiezoelectric material may be single crystal material. According to someembodiments, the mechanical resonating structure may comprise a base onwhich additional structures (e.g., electrodes) are formed, and the basemay comprise any of those materials listed, or any other suitablematerials.

According to some embodiments, the mechanical resonating structurecomprises or is formed of multiple layers, making the structure acomposite structure. For example, as mentioned, the mechanicalresonating structure 102 may comprise a base on which electrodes areformed, thus making the structure a composite structure. In addition, oralternatively, the base itself may comprise one or more layers ofdiffering materials, shapes, and/or thicknesses. For example, the baseof the mechanical resonating structure may comprise an active layer andone or more insulating layers.

The mechanical resonating structure may have any shape. For example,aspects of the technology may apply to mechanical resonating structuresthat are substantially rectangular (as shown in FIG. 2), substantiallyring-shaped, substantially disc-shaped, or that have any other suitableshape. Moreover, the mechanical resonating structure may have one ormore beveled edges. According to some embodiments, the mechanicalresonating structure may be substantially planar, such as the mechanicalresonating structure 102 of FIG. 2.

The mechanical resonating structures described herein may have anysuitable dimensions, and in some embodiment may be micromechanicalresonating structures. According to some embodiments, the mechanicalresonating structure 102 has a thickness T, which in some embodiments isless than approximately three wavelengths of a resonance frequency ofinterest of the mechanical resonating structure. According to someembodiments, the thickness is less than approximately two wavelengths ofthe resonance frequency of interest. In still other embodiments, thethickness may be less than approximately one wavelength of the resonancefrequency of interest (e.g., less than approximately one wavelength of aresonant Lamb wave supported by the mechanical resonating structure).The thickness may determine or depend on the types of waves supported bythe mechanical resonating structure. For example, a given thickness maylimit the ability of the mechanical resonating structure to support Lambwaves, or certain modes of Lamb waves. Thus, it should be appreciatedthat the thickness may be chosen in dependence on the types and/or modesof waves desired to be supported by the mechanical resonating structure.It should also be appreciated that thickness values other than thoselisted may be suitable for some applications, and that the variousaspects described herein are not limited to using mechanical resonatingstructures having any particular thickness values.

According to some embodiments, the mechanical resonating structuresdescribed herein have a large dimension (e.g., the largest of length,width, diameter, circumference, etc.) of less than approximately 1000microns, less than 100 microns, less than 50 microns, or any othersuitable value. It should be appreciated that other sizes are alsopossible. According to some embodiments, the devices described hereinform part or all of a microelectromechanical system (MEMS), for examplewith the mechanical resonating structure being a micromechanicalresonating structure.

The mechanical resonating structures may have any desired resonancefrequency or frequencies, as the various aspects described herein arenot limited to use with structures having any particular operating rangeor resonance frequency. For example, the resonance frequency of themechanical resonating structures may be between 1 kHz and 10 GHz. Insome embodiments, the frequencies of operation of the mechanicalresonating structure are in the upper MHz range (e.g., greater than 100MHz), or at least 1 GHz (e.g., between 1 GHz and 10 GHz). In someembodiments, the output signal produced by the mechanical resonatingstructures may have a frequency of at least 1 MHz (e.g., 13 MHz, 26 MHz)or, in some cases, at least 32 kHz. In some embodiments, the operatingfrequency may range from 30 to 35 kHz, 60 to 70 kHz, 10 MHz to 1 GHz, 1GHz to 3 GHz, 3 GHz to 10 GHz, or any other suitable frequencies.

The mechanical resonating structure 102 may be actuated and/or detectedin any suitable manner, with the particular type of actuation and/ordetection depending on the type of mechanical resonating structure, thedesired operating characteristics, or any other suitable criteria. Forexample, suitable actuation and/or detection techniques include, but arenot limited to, piezoelectric techniques, electrostatic techniques,magnetic techniques, thermal techniques, piezoresistive techniques, anycombination of those techniques listed, or any other suitabletechniques. The various aspects of the technology described herein arenot limited to the manner of actuation and/or detection.

According to some embodiments, the mechanical resonating structuresdescribed herein may be piezoelectric Lamb wave devices, such aspiezoelectric Lamb wave resonators. Such Lamb wave devices may operatebased on propagating acoustic waves, with the edges of the structure(e.g., the edges of mechanical resonating structure 102) serving asreflectors for the waves. For such devices, the spacing between theplate edges may define the resonance cavity, and resonance may beachieved when the cavity is an integer multiple of p, where p=λ/2, withλ being the acoustic wavelength of the Lamb wave. However, it should beappreciated that aspects of the technology described herein apply toother types of structures as well, and that Lamb wave structures aremerely non-limiting examples.

According to some embodiments, the devices comprise a mechanicalresonating structure. Suitable mechanical resonating structures havebeen described, for example, in PCT Patent Publication No. WO2006/083482, and in U.S. patent application Ser. No. 12/142,254, filedJun. 19, 2008 and published as U.S. Patent Publication 2009-0243747-A1,both of which are incorporated herein by reference in their entireties.However, such examples are non-limiting, as various other types ofmechanical resonators and mechanical resonating structures mayalternatively be used.

As mentioned with respect to FIG. 1, some embodiments include suspendedmechanical resonating structures. The structures may be suspended inthat they may have one or more segments which are not directly attachedto any other structures. For example, in FIG. 2 the ends of themechanical resonating structure 102 are not directly attached to thesubstrate 110. It should be appreciated that various forms of“suspended” structures may be used, including, but not limited to,structures having any one or more free surfaces.

As previously mentioned, mechanical resonating structures describedherein may have any suitable type, number, and configuration ofelectrodes, as the electrode 108 represents only one non-limitingexample. For example, the electrodes may be formed of any suitablematerial. Any number of electrodes may be included. For example, in someembodiments, one electrode is connected to each of an input port and anoutput port to drive and sense the operation of the mechanicalresonating structure. In other embodiments, more than one electrode maybe connected to each electrical port. In some embodiments, theelectrodes are individual strips. However, the electrodes may take anysuitable shape. For example, two or more of the electrodes (e.g.,electrodes 305 a and 305 b in FIG. 3C) may form a single electrode insome embodiments. The electrodes may extend along substantially theentire width W of a mechanical resonating structure, or mayalternatively extend along only a part of the width (e.g., half thewidth, a quarter of the width, etc.). Other configurations are alsopossible, as the various structures herein including electrodes are notlimited to any particular number, shapes, or configurations ofelectrodes, unless so stated.

As shown in FIG. 1, in some embodiments a device may include a capwafer, e.g., cap wafer 114. The cap wafer may facilitate formation of avacuum environment for the mechanical resonating structure, or may serveany other suitable function. In some embodiments, as shown, the capwafer 114 may include integrated circuitry. In some embodiments, the capwafer may be a CMOS wafer, and the integrated circuitry formed thereonmay be CMOS circuitry.

In some alternative embodiments, the cap wafer may not includeintegrated circuitry. Rather, the substrate 110 may itself includeintegrated circuitry, for example to control operation of the mechanicalresonating structure, to control the operation of the heating elementsand temperature sensors, or for any other reason. In some embodiments,both the substrate 110 and the cap wafer 114 may include integratedcircuitry. Thus, the various aspects and devices described herein arenot limited to use with any particular type and configuration of capwafer and/or substrate.

According to one aspect, the resonance frequency of a device ormechanical resonating structure is controlled both by controlling thetemperature using one or more of the techniques described herein and byelectrically controlling the resonance frequency of the structure. Forexample, the resonance frequency of a mechanical resonating structuremay be tuned in some embodiments by adjusting capacitances and/orinductances of circuitry connected to the mechanical resonatingstructure, and/or by adjusting a phase or frequency of a signal input tothe mechanical resonating structure. Such techniques may be combinedwith one or more of the temperature control techniques described hereinto facilitate accurate control of the operation of the mechanicalresonating structure, for example by controlling the resonance frequencyof the mechanical resonating structure.

The devices described herein may be used as stand alone components, ormay be incorporated into various types of larger devices. Thus, thevarious structures and methods described herein are not limited to beingused in any particular environment or device. However, examples ofdevices which may incorporate one or more of the structures and/ormethods described herein include, but are not limited to, tunablemeters, mass sensors, gyroscopes, accelerometers, switches, andelectromagnetic fuel sensors. According to some embodiments, themechanical resonating structures described are integrated in a timingoscillator. Timing oscillators are used in devices including digitalclocks, radios, computers, oscilloscopes, signal generators, and cellphones, for example to provide precise clock signals to facilitatesynchronization of other processes, such as receiving, processing,and/or transmitting signals. In some embodiments, one or more of thedevices described herein may form part or all of a MEMS.

Having thus described several aspects of at least one embodiment of thetechnology, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art. Such alterations, modifications, and improvements are intendedto be within the spirit and scope of the technology. Accordingly, theforegoing description and drawings provide non-limiting examples only.

In addition, while some references have been incorporated herein byreference, it should be appreciated that the present applicationcontrols to the extent the incorporated references are inconsistent withwhat is described herein.

What is claimed is:
 1. A device, comprising: a piezoelectric mechanicalresonating structure formed at least partially of a piezoelectricmaterial and including: a heating element configured to control atemperature of the piezoelectric mechanical resonating structure, theheating element comprising a metal or a doped semiconductor, and atemperature sensor configured to detect the temperature of themechanical resonating structure.
 2. The device of claim 1, wherein thepiezoelectric mechanical resonating structure has a largest dimension ofless than approximately 1000 microns.
 3. The device of claim 1, whereinthe heating element comprises a conductive trace formed of the metal. 4.The device of claim 1, wherein the heating element comprises aconductive trace formed of the doped semiconductor.
 5. The device ofclaim 1, wherein the heating element comprises the metal.
 6. The deviceof claim 1, wherein the heating element comprises the dopedsemiconductor.
 7. The device of claim 1, wherein the heating elementcomprises an electrode of the piezoelectric mechanical resonatingstructure.
 8. The device of claim 7, wherein the electrode is a firstelectrode and wherein temperature sensor comprises a second electrode ofthe mechanical resonating structure.
 9. The device of claim 1, whereinthe temperature sensor comprises a conductive trace.
 10. The device ofclaim 9, wherein at least part of the conductive trace is formed of ametal.
 11. The device of claim 9, wherein at least part of theconductive trace is formed of a conductive semiconductor material. 12.The device of claim 1, wherein the temperature sensor comprises anelectrode of the mechanical resonating structure.
 13. The device ofclaim 1, wherein the heating element and temperature sensor areconfigured in a feedback loop.
 14. The device of claim 13, furthercomprising temperature control circuitry coupled to the temperaturesensor and the heating element, and configured to receive an outputsignal of the temperature sensor indicative of the temperature of thepiezoelectric mechanical resonating structure and to provide a controlsignal to the heating element to adjust an amount of heat produced bythe heating element to set the temperature of the piezoelectricmechanical resonating structure to a target value.
 15. The device ofclaim 1, further comprising a cap wafer capping the piezoelectricmechanical resonating structure.
 16. The device of claim 1, wherein thetemperature sensor is a first temperature sensor, and wherein the devicefurther comprises a second temperature sensor.